If two conducting spheres are separately charged and then brought in contact,which of the following statements is true?

Two insulated charged conducting spheres of radii $20\,cm$ and $15\,cm$ respectively and having an equal charge of $10\,C$ are connected by a copper wire and then they are separated. Then

Assertion: $A$ metallic shield in the form of a hollow shell may be built to block an electric field.
Reason: In a hollow spherical shield,the electric field inside it is zero at every point.

Charge on the outer sphere is $q$ and the inner sphere is grounded. The charge on the inner sphere is $q'$,for $(r_2 > r_1)$. Then

Shown in the figure are two point charges $+Q$ and $-Q$ inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If $\sigma_1$ is the surface charge density on the inner surface and $Q_1$ is the net charge on it,and $\sigma_2$ is the surface charge density on the outer surface and $Q_2$ is the net charge on it,then:

Two metal spheres of radius $R$ and $3R$ have the same surface charge density $\sigma$. If they are brought in contact and then separated,the surface charge density on the smaller and bigger sphere becomes $\sigma_1$ and $\sigma_2$,respectively. The ratio $\frac{\sigma_1}{\sigma_2}$ is: